1. Field of the Invention
The present invention relates to a flow control valve to control hot water flow and a hot-water type heater apparatus employing the same, and particularly to such devices employed in a hot-water type heater apparatus for automotive use.
2. Description of Related Art
As a method of controlling the temperature of blown air of an automotive air-conditioning apparatus including a hot-water type heater apparatus, the technique of controlling hot water flow to a heat exchanger for heater use and of controlling a blown air temperature is known. This hot water flow control method has the following advantages in comparison with an air-mix method of controlling a blown air temperature which controls a mixing ratio of chilled air and warmed air by an air-mix damper.
With the hot-water flow control method, space for mixing chilled air and warmed air is not required, and so the volume of the air-duct system can be decreased by a corresponding amount, and there are also other advantages such as the ability to alleviate air resistance by eliminating the mixing space and the ability to reduce blower electrical power and wind noise.
Japanese Patent Application Laid-Open No. Sho. 64-145472 discloses a control valve for controlling hot-water flow by the foregoing hot-water flow control method. This device includes a hot water inlet into which hot water flows from an engine, a hot-water outlet through which hot water flows out toward a heat exchanger for heater use, and a bypass outlet through which hot water to flows out toward a bypass circuit of the heat exchanger for heater use in a hot water flow control valve housing.
Accordingly, a tubular needle valve to control hot water flow to the hot water outlet and the bypass outlet is disposed rotatably within the valve housing, and along with this, a pressure-responsive valve which is opened by a rise in hot water pressure is provided in the bypass circuit. When engine speed rises and hot water pressure rises, the pressure-responsive valve opens and hot water flows into the bypass circuit side as well, by which an excessive increase in hot water flow to the hot water outlet is prevented.
In this way, occurrence of unpleasant flow noise in the passage restricting portion of the needle valve portion is prevented by preventing an excessive increase of hot water flow to the hot water outlet.
A hot-water type heater apparatus has a characteristic of a sudden rise in blown-air temperature in a minute-flow region of hot water, as is known from the heat-radiating characteristics of a heat exchanger for heater use, and so if the minute-flow region of hot water is not controlled with accuracy, it becomes impossible to control blow-air temperature as desired, producing a fatal defect in practical use.
Nevertheless, the foregoing prior art device only controls an opening surface area of a hot-water outlet simply using a needle valve, and so in order to control minute flow it becomes necessary to form an opening portion of minute surface area in a portion of the control passages formed in the needle valve.
However, this minute opening portion is not only difficult to machine, but foreign matter such as casting sand contained in the hot water may clog the minute opening portion during minute flow control, thereby producing a state wherein minute flow cannot be controlled. Additionally, because hot water flow at the minute opening portion is restricted suddenly, the differential pressure between the areas before and after the minute opening portion becomes large, and there is also a problem of increased production of flow noise.